Such indwelling catheters usually comprise a housing with a housing interior which runs in the longitudinal direction of the housing and extends between a front and a rear opening of the housing and is optionally connected to an injection valve formed in the region of the housing wall, via which injection valve drugs in liquid form can be administered to the patent following placement of the indwelling catheter. A cannula for puncturing the skin during the placement of the indwelling catheter is introduced into the housing interior. The cannula is introduced into the housing interior until an entry opening in the region of a tip of the cannula is arranged outside the housing and in front of the front opening. A rear end of the cannula is arranged in a grip piece, by means of which the cannula can be guided as it is introduced into the housing and as it is removed from the housing. The grip piece is usually inserted into a rear end of the housing when the cannula is introduced into the housing for placement of the indwelling catheter. A channel is formed in the grip piece and is connected to the exit opening at the rear end of the cannula.
Various closure or connection pieces, for example a Luer connection system, can be inserted into an end of the grip piece remote from the housing, in order to close the channel in the grip piece and/or connect it to other lines. During placement of the indwelling catheter, usually a closure piece is arranged in the rear end of the grip piece, wherein the interior of the closure piece is connected at one side to the channel in the grip piece and thus to the exit opening of the cannula and at the other side to an outflow opening. Arranged in the region of the outflow opening is an air-permeable filter, through which air can flow out when blood flows from the channel in the grip piece into the closure piece and thereby displaces the air. After placement of the indwelling catheter, usually the closure piece and the grip piece containing the cannula are removed, so that other connections can be connected to the housing in order to further treat the patient.
Indwelling catheters having a structure such as this are known in various embodiments. Usually, a support is also formed on the housing of the indwelling catheter, for example in the form of laterally protruding wings, in order to support the indwelling catheter on the skin of the patient.
Indwelling catheters are used both in the field of stationary patient treatment and in connection with treating patients in an emergency or disaster. When treating badly injured patients, there is often a need for emergency transfusions, particularly with erythrocyte concentrates, immediately after the patient has been admitted to the stationary treatment center. These may then lead to massive transfusions. In this case, it is necessary to be able to carry out the transfusion as quickly as possible using ABO-compatible stored supplies. This standard means that it is necessary to determine the emergency blood group (antigen determination on receiver erythrocytes). For this, just 0.1-0.5 ml of natural blood from the patient is required. Practice shows that emergency medical treatment by transfusion is made more difficult by the following circumstances:                Infusion with the plasma expander hydroxyethyl starch (HES), which is used to treat shock at the site of the accident, makes it more difficult to reliably determine the blood group or may even make this impossible within a short time since HES molecules can agglutinate with high-molecular-weight erythrocytes (pseudoagglutination).        Patients in severe hemorrhagic shock receive so-called “O Rh negative emergency blood supplies” immediately after being admitted to the rescue center. After the transfusion of emergency blood supplies, the patient's blood group can no longer be reliably determined (mixed field agglutination). Further treatment can then no longer take place with ABO-compatible blood supplies but rather must take place with supplies of blood group O. In particular, treatment of a number of patients at the same time or transfusion management in the event of a disaster or treatment of a number of patients at the same time is made more difficult as a result.        Ideally, the pretransfusion blood sample to determine the emergency blood group would be taken at the mobile site within the context of primary treatment. However, practice in rescue medicine shows that this does not happen since the priority is to ensure vital functions of the patient. The filling, clear identification and storing of test tubes of blood is a task that cannot be performed in practice during primary treatment in an emergency. For most patients, therefore, blood is not taken until the patient is delivered to the stationary treatment center.        
Patients with severe hemorrhagic shock are the most likely to be affected by the risk of the blood group not being determined or not being clearly determined in the event of an emergency. These patients require plasma expanders in large quantity and emergency blood supplies with the greatest urgency.